Fluids and drugs are frequently administered to patients by intravenous infusion, also known as IV therapy. For IV therapy administration, a bag of IV solution is usually hung above a patient. Gravity pulls the IV solution downwards through a flexible line of delivery tubing to a venipuncture site on the patient, often in the forearm, wrist, or hand. To control the rate at which the IV solution is delivered to the patient, a pinch valve or roller clamp can be included on the outer surface of the tubing. Pinch valves and roller clamps compress the tubing to progressively restrict the flow of the IV solution reaching the patient's vein.
Even after a particular IV solution delivery rate is set with a pinch valve or roller clamp, substantial deviations in the flow rate can be observed. For example, as IV therapy progresses, the amount of IV solution remaining within the IV bag will be reduced. Along with this reduction in volume, the head pressure acting on the remaining IV solution is reduced and therefore, flow rate slows. Unwanted changes in flow rate can also be caused by changes in elevation of the IV bag or simple movement of a patient's limb. Indeed, Bernoulli's principle teaches that the total energy at a given point in a fluid is the energy associated with the movement of the fluid, plus energy from pressure in the fluid, plus energy from the height of the fluid relative to an arbitrary datum. Working knowledge of Bernoulli's principle, however, does not lead to a perfect pressure compensating flow rate controlling device. Pressure head variations are unpredictable and remain difficult to manage in IV therapy administration.